Water reducible quaternary ammonium salt containing polymers

ABSTRACT

This invention relates to a water dispersible coating composition which comprises: 
     (i) an acrylic polymer having active hydrogen functionality and quaternary ammonium salt functionality; and 
     (ii) a blocked polyisocyanate. 
     The water dispersible coating composition of this invention can be applied by any means known within the coatings art, but is especially suited for use in cathodic electrodeposition.

This application is a division of application Ser. No. 431,995, filedSept. 30, 1982, now U.S. Pat. No. 4,444,955.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a water dispersible coating composition whichcomprises:

(i) an acrylic polymer having active hydrogen functionality andquaternary ammonium salt functionality; and

(ii) a blocked polyisocyanate.

The water dispersible coating composition of this invention can beapplied by any means known within the coatings art, but is especiallysuited for use in cathodic electrodeposition.

2. Description of the Prior Art

The use of quaternary ammonium salt containing polymers as waterreducible coatings has been known in the art. For example, U.S. Pat. No.3,935,087 teaches resins prepared by reacting a portion of the hydroxylgroups of a hydroxyl-containing epoxy group-containing organic materialwith a partially-capped or blocked organic polyisocyanate, followed byreacting at least a portion of the epoxy groups in a manner so as to addpendant quaternary onium salt groups to render the resin waterdispersible or solubilized.

U.S. Pat. No. 4,071,428 teaches electrodepositable compositions whichcomprise the reaction product of a polymeric tertiary amine and a 1,2epoxy containing material in the presence of acid and/or water to formquaternary ammonium base group-containing polymers. This approach hasthe drawback that the epoxy could also react with other functionalgroups on the polymer backbone, such as hydroxyl groups or primary andsecondary amine groups.

BRIEF SUMMARY OF THE INVENTION

This invention relates to a water dispersible coating composition whichcomprises:

(i) an acrylic polymer which comprises the free radical addition productof (a) at least one quaternary ammonium salt containing monomer havingthe structure: ##STR1## wherein R₁ is H or alkyl of 1 to 3 carbons; Z isN--H or O; R₂ is a divalent methylene radical --(CH₂)_(n) --, wherein nis an integer from 1 to about 10; R₃, R₄ and R₅ can be the same ordifferent and are alkyl or substituted alkyl, preferably of 1 to about20 carbons or aryl or substituted aryl, preferably of 6 to about 18carbons with the proviso that R₃, R₄ and R₅ cannot be hydroxyfunctional; and X⁻ is an anion; and (b) at least one active hydrogenfunctional unsaturated monomer; and (c) at least one other ethylenicallyunsaturated monomer; and

(ii) a blocked polyisocyanate which is stable in the presence of theacrylic polymer at room temperature but reactive with the acrylicpolymer at elevated temperatures.

It is especially preferred to have R₃, R₄ and R₅ all lower alkyl of 1 to4 carbons. Substituted alkyl or aryl groups are those having one or morehydrogen atoms replaced with alkyl, aryl, aroxy, alkoxy or halogengroups and can contain acyl groups.

The quaternary ammonium salt groups on the acrylic polymer backbone havea catalytic effect providing lower temperature cures with the blockedpolyisocyanate.

This invention also relates to a method of electrocoating anelectrically conductive surface serving as a cathode in an electricalcircuit comprising said cathode, an anode, and an aqueouselectrodepositable composition wherein the aqueous electrodepositablecomposition comprises the coating described above.

Accordingly, it is an object of this invention to provide improved waterreducible coatings. It is a further object of this invention to providewater reducible coatings having excellent exterior durability. Anotherobject of this invention is to provide water reducible coatings havingexcellent low temperature cure response with blocked isocyanates.Another object of this invention is to provide a method ofelectrocoating an electrically conductive surface. These and otherobjects of this invention will be apparent from the followingdiscussions.

DETAILED DESCRIPTION OF THE INVENTION

The acrylic polymers useful in the practice of this invention containone or more active hydrogen containing groups as determined by theZerewitinoff Method as described by Kohler in J. Am. Chem. Soc, 49, 3181(1927). Some such suitable compounds are, for example, acrylic polymershaving one or more of any of the following types of active hydrogencontaining groups, among others, --OH, --NH₂, --NH, --CONH--, --COOH,--SH and the like.

The acrylic polymers are prepared by conventional free radical additionpolymerization techniques and can use any suitable unsaturated monomers.Methods of producing acrylic polymers are well known and are not a partof the present invention. If desired the free radical polymerization canbe catalyzed by conventional catalysts known in the art such as azo,peroxy or redox catalysts. Typically the acrylic polymers are producedby heating the unsaturated monomers at temperatures ranging from about180° F. to 450° F. and especially 200° F. to about 300° F. to effect thepolymerization. It is normally preferred to prepare the acrylic polymersby solution polymerization in organic solvents. Solvents having asolubility of at least about 30 grams per liter of water are preferred.Especially preferred are the glycol ethers and glycol ether esters suchas ethylene glycol monoethyl ether, diethylene glycol monobutyl ether,2-ethoxyethyl acetate etc. If it is desired to achieve a relatively lowmolecular weight acrylic polymer, a chain transfer agent such as amercaptan may be employed to achieve this result.

Especially preferred in the practice of this invention is an acrylicpolymer which comprises the free radical addition product of (a) fromabout 1 to about 10% of at least one quaternary ammonium salt containingmonomer having the structure: ##STR2## wherein R₁ is H or alkyl of 1 to3 carbons; Z is N--H or O; R₂ is a divalent methylene radical--(CH₂)_(n) --, wherein n is from 1 to about 10; R₃, R₄ and R₅ can bethe same or different and are alkyl or substituted alkyl, preferably of1 to about 20 carbons or aryl or substituted aryl, preferably of 6 toabout 18 carbons with the proviso that R₃, R₄ and R₅ cannot be hydroxyfunctional; and X⁻ is an anion; and (b) from about 1 to about 20% of atleast one tertiary amine containing unsaturated monomer; and (c) fromabout 5 to about 30% of at least one active hydrogen functionalunsaturated monomer; and (d) from about 40 to about 93% of at least oneother ethylenically unsaturated monomer. It is especially preferred inthe practice of this invention to use a hydroxy functional monomer asthe active hydrogen functional monomer.

The quaternary ammonium salt containing unsaturated monomers having thestructure (I) can be prepared by many methods known in the art forproducing quaternary ammonium salts from amines. They are typicallyprepared by reacting an unsaturated tertiary amine having the structure:##STR3## with an alkylating agent R₅ X under conditions producing thequaternary ammonium salt. The anion X⁻ in the quaternary ammoniumcontaining monomer will typically be the anion obtained by removing thealkyl groups from the alkylating agent.

The alkylating agent can be any alkylating agent which will react withthe tertiary amine to produce the quaternary ammonium salt withoutreacting with the unsaturation or other functional groups on thetertiary amine containing monomer. Especially preferred as alkylatingagents are the alkyl halides and the dialkyl sulfates. Representativeexamples of useful alkyl halides includes methyl chloride, ethylbromide, n-propyl iodide, tertiary butyl chloride and benzyl chlorideand the like. Preferred dialkyl sulfates include dimethyl sulfate,diethyl sulfate, and the like. The alkylation reactions typically takeplace readily by admixing at essentially stoichiometric amounts of thereactants under relatively mild conditions (approximately 60° C. orlower) and are usually conducted in aqueous or lower alcohol solvents.

Preferred quaternary ammonium salt-containing unsaturated monomers forthe practice of this invention include: ##STR4## (conveniently preparedby the reaction of dimethylaminoethyl methacrylate and dimethylsulfate);##STR5## (conveniently prepared by the reaction of dimethylaminoethylmethacrylate and methyl chloride); ##STR6## (conveniently prepared bythe reaction of dimethylaminopropyl methacrylamide and methyl chloride.)

Useful active hydrogen functional unsaturated monomers include thehydroxy-functional monoesters typically prepared by the reaction ofdiols with unsaturated acids such as hydroxyesters of acrylic ormethacrylic acid wherein the hydroxyalkyl group contains up to about 6carbon atoms such as 2-hydroxyethyl acrylate, 2-hydroxyethylmethacrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl acrylate,3-hydroxypropyl methacrylate, 4-hydroxybutyl methacrylate, diethyleneglycol methacrylate and so forth. Corresponding esters of otherunsaturated acids, for example, crotonic acid, maleic acid, and similaracids of up to about 6 carbon atoms can also be employed. Also useful asactive hydrogen functional unsaturated monomers are the ethylenicallyunsaturated amides such as acrylamide, methacrylamide, and other similarmaterials.

If desired, primary or secondary amine functionality can also beincorporated as active hydrogen functionality into the acrylic polymer.Primary or secondary amines will impart a cationic charge to the polymerwhen neutralized by an acid and, by virtue of their active hydrogens,also become a site for accepting crosslinks when the coating containingthe blocked isocyanate is cured.

Typical primary and secondary amine compounds which can be incorporatedinto the acrylic polymers include amine-containing esters ofmonofunctional unsaturated acids of the formula: ##STR7## wherein R₆ ishydrogen, alkyl of 1 to about 10 carbon atoms, or aryl of 6 to about 12carbon atoms; R₇ is --(CH₂)_(n) -- with n having a value of about 1 to6; and R₈ is hydrogen or an alkyl group of from 1 to about 3 carbonatoms. Examples of such materials include acrylic or methacrylic estersof alcohols having pendant primary or secondary amines such as theesters of ethanol amine, t-butylamino ethanol, and the like.

Useful tertiary amine containing unsaturated monomers include theacrylates, such as 2-(N,N-dimethylamino)ethylacrylate,2-(N,N-diethylamino)ethylacrylate, 2-(N,N-dimethylamino)propylacrylateand the like; the methacrylates such as2-(N,N-dimethylamino)ethylmethacrylate,2-(N,N-diethylamino)ethylmethacrylate and the like; the acrylamides,such as 2-(N,N-dimethylamino)ethylacrylamide and2-(N,N-dimethylamino)ethylmethacrylamide and the like; vinyl compoundssuch as N-vinyl piperidine and the like.

When the acrylic polymer contains primary, secondary or tertiary aminegroups, these groups can be, if desired, neutralized with acid toprovide additional water solubility and to facilitate deposition uponthe cathode during cathodic electrodeposition. The total amount ofquaternary ammonium salt and/or neutralized amine need only besufficient to provide water dispersibility to the polymer. If it isdesired to neutralize some of the primary, secondary or tertiary aminegroups in the polymer this can be readily accomplished by reacting allor part of the amino groups with an acid such acetic acid, lactic acid,phosphoric acid, formic acid, citric acid or the like.

Other useful ethylenically unsaturated monomers include those which aresubstantially free of tertiary amine or quaternary ammonium saltfunctionality. These include the unsaturated hydrocarbons such asisoprene, butadiene, ethylene, styrene, substituted styrenes, etc.;vinyl compounds such as vinyl toluene, vinyl acetate, vinyl chloride,etc; esters of unsaturated acids such as butyl acrylate, butylmethacrylate, methyl methacrylate, isobutyl methacrylate, and so forth.

The blocked isocyanates which may be employed in this invention may beany isocyanate where the isocyanate groups have been reacted with acompound so that the resultant blocked isocyanate is stable in thepresence of the water reducible acrylic polymer at room temperature butis reactive with the acrylic polymer at elevated temperatures, usuallybetween about 150° F. and about 600° F. The blocked polyisocyanate willtypically be at a level of about 0.3 to about 3.0 equivalents ofisocyanate for each equivalent of active hydrogen.

In the preparation of the blocked organic polyisocyanate, any suitableorganic polyisocyanate may be used. Representative examples are thealiphatic compounds such as trimethylene, tetramethylene,pentamethylene, hexamethylene, 1,2-propylene, 1,2-butylene,2,3-butylene, 1,3-butylene, ethylidine and butylidene diisocyanates; thecycloalkylene compounds such as3-isocyanatomethyl-3,5,5-trimethylcyclohexylisocyanate, and the1,3-cyclopentane, 1,4-cyclohexane, and 1,2-cyclohexane diisocyanates;the aromatic compounds such as m-phenylene, p-phenylene, 4,4'-diphenyl,1,5-naphthalene and 1,4-naphthalene diisocyanates; thealiphatic-aromatic compounds such as 4,4'-diphenylene methane, 2,4- or2,6-toluene, or mixtures thereof, 4,4'-toluidine, and 1,4-xylylenediisocyanates; the nuclear substituted aromatic compounds such asdianisidine diisocyanate, 4,4'-diphenylether diisocyanate andchloro-diphenylene diisocyanate; the triisocyanates such as triphenylmethane-4,4',4"-triisocyanate, 1,3,5-triisocyanate benzene and2,4,6-triisocyanate toluene; and the tetraisocyanates such as4,4'-diphenyl-dimethyl methane-2,2'-5,5'tetraisocyanate; the polymerizedpolyisocyanates such as tolylene diisocyanate dimers and trimers, andother various polyisocyanates containing biuret linkages and/orallophanate linkages.

The blocked isocyanate may also be a prepolymer prepared by reacting apartially blocked isocyanate with an active hydrogen containingmolecule. For instance, the prepolymer may be derived from a polyolincluding polyether polyols, or polyester polyols, which are reactedwith excess partially blocked polyisocyanates. In this procedure, a lessthan stoichiometric amount of blocking agent is added to apolyfunctional isocyanate thereby blocking some but not all of theisocyanate groups available. The remaining isocyanate groups can then bereacted with a compound containing at least two active hydrogens toprepare the prepolymer.

As the blocking agent, any of the blocking agents known in the art maybe used in the practice of this invention. Typical examples of them arephenol types (e.g. phenol, cresol, xylenol, nitrophenol, chlorophenol,ethyl phenol, t-butylphenol, hydroxy benzoic acid, hydroxy benzoic acidesters, 2,5-di-t-butyl-4-hydroxy toluene, etc.), lactam types (e.g.ε-caprolactam, α-valerolactam, γ-butyrolactam, β-propiolactam, etc.),active methylene types (e.g. diethyl malonate, dimethyl malonate, ethylacetoacetate, methyl acetoacetate, acetyl acetone, etc.), alcohol types(e.g. methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol,t-butanol, n-amyl alcohol, t-amyl alcohol, lauryl alcohol, ethyleneglycol monomethyl ether, ethylene glycol monoethyl ether, ethyleneglycol monobutyl ether, diethylene glycol monomethyl ether, diethyleneglycol monoethyl ether, propylene glycol monomethyl ether,methoxymethanol, glycolic acid, glycolic acid esters, lactic acid,lactic acid esters, methylol urea, methylol melamine, diacetone alcohol,ethylene chlorohydrine, ethylene bromhydrine, 1,3-dichloro-2-propanol,acetocyanhydrine, etc.), mercaptan types (e.g. butyl mercaptan, hexylmercaptan, t-butyl mercaptan, t-dodecyl mercaptan,2-mercapto-benzothiazole, thiophenol, methyl thiophenol, ethylthiophenol, etc.), acid amide types (e.g. acetoanilide, acetoanisidineamide, acrylamide, methacrylamide, acetic amide, stearic amide,benzamide, etc.), imide types (e.g. succinimide, phthalimide, maleimide,etc.), amine types (e.g. diphenylamine, phenylnaphthylamine, xylidine,N-phenyl xylidine, carbazole, aniline, naphthylamine, butylamine,dibutylamine, butyl phenylamine, etc.), imidazole types (e.g. imidazole,2-ethylimidazole, etc.), urea types (e.g. urea, thiourea, ethylene urea,ethylene thiourea, 1,3-diphenyl urea, etc.), carbamate types (e.g.N-phenyl carbamic acid phenyl ester, 2-oxazolidone, etc.), imine types(e.g. ethylene imine, etc.), oxime types (e.g. formaldoxime,acetaldoxime, acetoxime, methylethyl ketoxime, diacetylmonoxime,benzophenonoxime, chlorohexanonoxime, etc.), sulfurous acid salt types(e.g. sodium bisulfite, potassium bisulfite, etc.), and hydroxamic acidester or acyl hydroxamate types (e.g. benzyl methacrylo hydroxamate(BMH), allyl methacrylo hydroxamate, etc.). The preparation and use ofhydroxamic acid ester or acyl hydroxamates as blocking agents isthoroughly disclosed in U.S. Pat. No. 4,008,192 issued to Mijs et al,the teaching of which is hereby incorporated by reference.

Among the possible blocking agents, it is especially preferred to usethe lactam types, the active methylene types, the oxime types, and thehydroxamic acid ester or acyl hydroxamate type blocking agents.

The blocked isocyanates are typically prepared by mixing the isocyanateand the blocking agent while maintaining the temperature between about50° to about 230° F.

The coating of this invention comprising the acrylic polymer and theblocked isocyanate can be dispersed in water and, usually, incombination with a water-miscible solvent. The concentration of thecoating in water depends upon the process parameters to be used and isin general not critical, but in the case of electrodeposition, the majorproportion of the aqueous composition will normally be water, e.g., thecomposition may contain about 1 to about 75% and typically 1 to about50% by weight solid coating with the remainder being water.

The coating of this invention may be applied by any means, includingelectrodeposition, spray, flow coating, curtain coating, roller coating,dipping, brushing, or other method known in the art.

In most instances, a pigment composition and, if desired, variousadditives such as catalysts, flow agents, dispersants, solvents, andother materials may be included in the coating composition. The pigmentcomposition may be of any conventional type, comprising, for example,one or more pigments such as iron oxides, lead oxides, strontiumchromate, carbon black, titanium dioxide, talc, barium sulfate, zincoxide, cadmium yellow, cadmium red, chromic yellow and the like.

In electrodeposition processes employing the aqueous coating compositiondescribed herein, the aqueous composition is placed in contact with anelectrically conductive anode and an electrically conductive cathode,with the surface to be coated being the cathode. Upon passage ofelectric current between the anode and the cathode, while in contactwith the bath containing the coating composition, an adherent film ofthe coating composition is deposited on the cathode. The applied voltagemay be varied greatly within the practice of this invention forelectrodeposition and can be, for example, as low as 1 volt or as highas several thousand volts, although typically between 50 volts and 500volts. The current density is usually between 1 ampere and 15 amperesper square foot, and tends to decrease during electrodeposition.

The electrodeposition method is applicable to the coating of anyelectrically conductive substrate, and especially metal such as steel,aluminum, copper, or surfaces which have been coated with conductiveprimers or filaments to impart a conductive surface.

After application by whatever means desired, the coating is cured atelevated temperatures by any convenient method such as in baking ovensor with banks of infared heat lamps. Curing temperatures are preferablyfrom about 150° F. to about 450° F. although somewhat higher or lowertemperatures can be employed if desired.

The following examples have been selected to illustrate specificembodiments and practices of advantage to a more complete understandingof the invention. Unless otherwise stated, "parts" means parts byweight.

EXAMPLE 1 Preparation of Blocked Isocyanate Prepolymer

A four necked flask equipped with Friedricks condenser, calcium chloridedrying tube, mechanical stirrer, nitrogen gas inlet, and heating mantlewas charged with 729.5 parts benzylmethacrylo hydroxamate (BMH)(prepared as described in U.S. Pat. No. 4,008,192, column 6, lines28-56) and heated to 180° F. until the BMH melted. To the molten BMH wasadded 626 parts Hylene®W (saturated version of methylenedi-para-phenylene isocyanate sold by E. I. duPont) and 600 partsn-methyl pyrrolidinone over a 2 hour period. The reaction mixture wasmaintained at 180° F. for an additional 2 hours. The temperature wasthen reduced to 130° F. and 9.5 parts dibutyl tin dilaurate was added tothe reaction mixture. The reaction mixture was held at 130° F. untilinfrared analysis indicated a constant isocyanate level. 43 parts oftrimethyol propane was gradually added to the reaction mixture over a 2hour period. The reaction mixture was held at this temperature untilinfrared analysis indicated that essentially all of the isocyanate wasreacted. The BMH-blocked isocyanate prepolymer product was a 70.12percent weight solids solution in the n-methyl pyrrolidinone solvent.

EXAMPLE 2 Preparation of Quaternary Ammonium Salt Containing AcrylicVehicle

A reaction vessel equipped with stirrer, condenser, and 2 additiondropping funnels was charged with 250 parts 2-butoxy ethanol and heatedto 250° F. A mixture of 179 parts styrene; 42.9 parts butyl acrylate;190 parts hydroxyethyl acrylate; 95 parts dimethylaminoethylmethacrylate; and 15 parts Vazo 64, (2,2'-azobis-(isobutyronitrile) freeradical initiator manufactured by E. I. duPont) was placed in one of thedropping funnels. The other dropping funnel was charged with 43.8 partsof a 80% aqueous solution of Sipomer®Q5-80 (quaternization product ofdimethylaminoethyl methacrylate and dimethyl sulfate sold by AlcolacInc.).

The contents of the 2 addition dropping funnels were addedsimultaneously to the heated solvent over about a 3 hour period. Themixture was maintained at 250° for about 15 minutes and then a solutionof 3.8 parts 2-butoxy ethanol and 1.9 parts Vazo 64 was added to thereaction mixture in 4 separate additions each 15 minutes apart. Thereaction mixture was held at 250° for approximately 3 hours and then thereaction vessel was attached to a Dean-Stark trap to remove the water.The acrylic vehicle produced by this reaction was approximately 74%weight solids.

EXAMPLES 3

Following the procedure of Example 2 an acrylic vehicle was preparedhaving a weight percent solids composition of 44.5% butyl acrylate;24.7% styrene; 19.8% hydroxyethyl acrylate; 7.8% dimethylaminoethylmethacrylate; and 3% methacrylamidopropyltrimethylammonium chloride(marketed as MAPTAC by Texaco Chemical Company).

In order to test pigmented formulations a grind paste was prepared bymixing on a laboratory mill:

Grind Paste

blocked isocyanate from Example 1: 596.75 parts

furnace black: 121.55 parts

Representative examples of coating formulations useful in cathodicelectrodeposition are described in Examples 4 and 5.

EXAMPLE 4

An aqueous coating was prepared by mixing the following ingredients:

Grind Paste: 54.4 parts

acrylic vehicle from Example 2: 153.4 parts

blocked isocyanate from from Example 1: 63.0 parts

lactic acid: 2.5 parts

2-ethoxyethyl acetate: 10.0 parts

distilled water: 1,716 parts

This coating was electrodeposited on a zinc phosphate panel cathodeusing a voltage of 150 volts for one minute. The panel was baked at 220°F. for 30 minutes to provide a hard, solvent resistant finish.

EXAMPLE 5

A cathodically electrodepositable coating was prepared by mixing:

Grind Paste: 54.5 parts

acrylic resin from Example 3: 160.9 parts

blocked isocyanate Cross-linker from Example 1: 153.0 parts

lactic acid: 2.5 parts

2-ethoxyethyl acetate: 10.0 parts

deionized water: 1716.0 parts.

A zinc phosphate treated steel panel used as the cathode waselectrodeposited with this coating for 60 seconds at 40 volts, rinsedwith water and baked 30 minutes at 220° F. to yield a hard, solventresistant finish.

While this invention has been described by a number of specificembodiments, it is obvious that other variations and modifications maybe made without departing from the spirit and scope of the invention asset forth in the appended claims.

The invention claimed is:
 1. The method of electrocoating anelectrically conductive surface serving as a cathode by passing anelectrical current through an electrical circuit comprising saidcathode, an anode, and an aqueous electrodepositable composition incontact with said cathode and said anode; wherein the electrodepositablecomposition comprises:(i) an acrylic polymer which comprises the freeradical addition product of: (a) at least one quaternary ammonium saltcontaining unsaturated monomer having the structure: ##STR8## wherein R₁is H or alkyl of 1 to 3 carbons; Z is N--H or O; R₂ is a divalentmethylene radical --(CH₂)_(n) -- wherein n is from 1 to about 10; R₃, R₄and R₅ can be the same or different and are alkyl, substituted alkyl,aryl or substituted aryl, with the proviso R₃, R₄ and R₅ cannot behydroxy functional; and X⁻ is an anion; and (b) at least one activehydrogen functional unsaturated monomer; and (c) at least one otherethylenically unsaturated monomer; and (ii) a blocked polyisocyanatewhich is stable in the presence of the acrylic polymer at roomtemperature but reactive with the acrylic polymer at elevatedtemperatures.
 2. The method of electrocoating of claim 1 furthercharacterized in that the active hydrogen functional unsaturated monomeris a hydroxy functional monomer.
 3. The method of electrocoating ofclaim 1 further characterized in that the acrylic polymer containsstyrene.
 4. The method of electrocoating of claim 1 furthercharacterized in that the blocked polyisocyanate is present at a levelof about 0.3 to about 3.0 equivalents of isocyanate for each equivalentof active hydrogen.
 5. The method of electrocoating of claim 1 furthercharacterized in that the blocked polyisocyanate is the reaction productof an organic polyisocyanate and a blocking agent selected from thegroup consisting of oximes, lactams, hydroxamic acid esters, and activemethylene blocking agents.
 6. The method of electrocoating of claim 5further characterized in that the blocking agent isbenzylmethacrylohydroxamate.
 7. The method of electrocoating of claim 1further characterized in that the quaternary ammonium salt containingmonomer is: ##STR9##
 8. The method of electrocoating of claim 1 furthercharacterized in that the quaternary ammonium salt containing monomeris: ##STR10##
 9. The method of electrocoating of claim 1 furthercharacterized in that the quaternary ammonium salt containing monomeris: ##STR11##
 10. The method of electrocoating an electricallyconductive surface serving as a cathode by passing an electrical currentthrough an electrical circuit comprising said cathode, an anode, and anaqueous electrodepositable composition in contact with said cathode andsaid anode; wherein the electrodepositable composition comprises:(i) anacrylic polymer which comprises the free radical addition product of:(a) from about 1 to about 10 percent of at least one quaternary ammoniumsalt containing unsaturated monomer having the structure: ##STR12##wherein R₁ is H or alkyl of 1 to 3 carbons; Z is N--H or O; R₂ is adivalent methylene radical --(CH₂)_(n) -- wherein n is from 1 to about10; R₃, R₄, and R₅ can be the same or different and are alkyl,substituted alkyl, aryl or substituted aryl, with the proviso that R₃,R₄ and R₅ cannot be hydroxy functional; and X⁻ is an anion; and (b) fromabout 1 to about 20 percent of at least one tertiary amine containingunsaturated monomer; and (c) from about 5 to about 30 percent of atleast one active hydrogen functional unsaturated monomer; and (d) fromabout 40 to about 93 percent of at least one other ethylenicallyunsaturated monomer; and (ii) a blocked polyisocyanate which is stablein the presence of the acrylic polymer at room temperature but reactivewith the acrylic polymer at elevated temperatures.
 11. The method ofelectrocoating of claim 10 further characterized in that the activehydrogen functional monomer is a hydroxy functional monomer.
 12. Themethod of electrocoating of claim 10 further characterized in that theacrylic polymer contains styrene.
 13. The method of electrocoating ofclaim 10 further characterized in that the blocked polyisocyanate ispresent at a level of about 0.3 to about 3.0 equivalents of isocyanatefor each equivalent of active hydrogen.
 14. The method of electrocoatingof claim 10 further characterized in that the blocked polyisocyanate isthe reaction product of an organic polyisocyanate and a blocking agentselected from the group consisting of oximes, lactams, hydroxamic acidesters, and active methylene blocking agents.
 15. The method ofelectrocoating of claim 14 further characterized in that the blockingagent is benzylmethacrylohydroxamate.
 16. The method of coating anelectrically conductive substrate serving as a cathode which methodcomprises passing an electrical current through an electrical circuitcomprising said cathode, an anode, and an aqueous electrodepositablecomposition in contact with said cathode and said anode thereby applyingan adherent film of the electrodepositable composition onto the surfaceof the substrate, and subsequently curing the electrodepositable coatingat elevated temperatures; wherein the electrodepositable compositioncomprises:(i) an acrylic polymer which comprises the free radicaladdition product of: (a) at least one quaternary ammonium saltcontaining unsaturated monomer having the structure: ##STR13## whereinR₁ is H or alkyl of 1 to 3 carbons; Z is N--H or O; R₂ is a divalentmethylene radical --(CH₂)_(n) -- wherein n is from 1 to about 10; R₃, R₄and R₅ can be the same or different and are alkyl, substituted alkyl,aryl or substituted aryl, with the proviso R₃, R₄ and R₅ cannot behydroxy functional; and X⁻ is an anion; and (b) at least one activehydrogen functional unsaturated monomer; and (c) at least one otherethylenically unsaturated monomer; and (ii) a blocked polyisocyanatewhich is stable in the presence of the acrylic polymer at roomtemperature but reactive with the acrylic polymer at elevatedtemperatures.
 17. A substrate coated by the method of claim
 16. 18. Themethod of coating an electrically conductive substrate serving as acathode which method comprises passing an electrical current through anelectrical circuit comprising said cathode, an anode, and an aqueouselectrodepositable composition in contact with said cathode and saidanode thereby applying an adherent film of the electrodepositablecomposition onto the surface of the substrate, and subsequently curingthe electro-depositable coating at elevated temperatures; wherein theelectro-depositable composition comprises:(i) an acrylic polymer whichcomprises the free radical addition product of: (a) from about 1 toabout 10 percent of at least one quaternary ammonium salt containingunsaturated monomer having the structure: ##STR14## wherein R₁ is H oralkyl of 1 to 3 carbons; Z is N--H or O; R₂ is a divalent methyleneradical --(CH₂)_(n) -- wherein n is from 1 to about 10; R₃, R₄, and R₅can be the same or different and are alkyl, substituted alkyl, aryl orsubstituted aryl, with the proviso that R₃, R₄ and R₅ cannot be hydroxyfunctional; and X⁻ is an anion; and (b) from about 1 to about 20 percentof at least one tertiary amine containing unsaturated monomer; and (c)from about 5 to about 30 percent of at least one active hydrogenfunctional unsaturated monomer; and (d) from about 40 to about 93percent of at least one other ethylenically unsaturated monomer; and(ii) a blocked polyisocyanate which is stable in the presence of theacrylic polymer at room temperature but reactive with the acrylicpolymer at elevated temperatures.
 19. A substrate coated by the methodof claim 18.